== Introduction ==
[[File:HistologicChapter12Liver.jpg|thumb|200px|Liver Lobe]]
The liver functions as a vast biosynthetic chemical factory, synthesizing large complex molecules from substances brought to it in the blood, particularly substances recently absorbed by the intestine and transported by the portal blood system. All of the biochemical functions of the liver are carried out by the epithelial parenchymal cells of the liver, the hepatocytes. Hepatocytes are responsible for bile synthesis and secretion, excretion of bilirubin, protein carbohydrate and lipid metabolism, storage (vitamins A, D and B12 and iron as ferritin), and conjugation and elimination of metabolites and toxins.
=== Blood Supply to a Lobule ===
[[File:HistologicChapter12Liver2.jpg|thumb|200px|Liver]]
At the periphery of the lobules, in the angles between 2 or 3 adjacent lobules, lie the interlobular septa or portal canals consisting of connective tissue, and containing a branch of the hepatic artery, a branch of the portal vein, a small bile duct, a lymphatic vessel and small nerves. The blood that enters a lobule is supplied from the vessels in the portal system. Both venous and arterial blood enters a lobule. The venous blood enters the sinusoids directly from the smallest branches of the portal vein. Only a small volume of arterial blood enters the sinusoids directly from the smallest branches of the hepatic artery. Most of the arterial blood goes through a capillary bed to enter the small branches of the portal vein before going on to the sinusoids. Blood in the sinusoids “bathes” the hepatocytes before passing into the central vein from which it flows into a sublobular (intercalated) vein. Sublobular veins progressively unite to form the collecting veins that progressively join to form the hepatic veins. Two or more hepatic veins empty directly into the inferior vena cava.
Remember that lymph and bile flow from a lobule in a direction opposite to the flow of blood in the sinusoids.
==== Slide 152, Liver and Gallbladder (H&E) ====
<peir-vm>UAB-Histology-00152</peir-vm>
== Gallbladder ==
[[File:HistologicChapter12GallbladderDiagram.jpg|thumb|200px|Gallbladder Diagram]]
The pear-shaped gallbladder shows marked variation in size and shape among different individuals. Anatomically, it consists of a neck, a body, and a blindly ending fundus. Histologically, its wall consists of a mucosa, a muscularis, a perimuscular layer of connective tissue, and a serosa or fibrosa.
1. === Slide 151 gallbladderGallbladder, (H&E)===
a. Mucosa - The mucosa consists of an epithelium, its basement membrane, and an underlying lamina propria of loose connective tissue. The tall, simple columnar epithelial cells of the mucosa are absorptive in nature. They have basal ovoid nuclei and on their luminal surface is a thin striated border (demonstrated by EM). No goblet cells are present in this epithelium. The mucosa of the non-distended gallbladder is irregularly folded, somewhat resembling villi when it is sectioned. These folds largely disappear when the gallbladder is filled.
Simple tubuloalveolar glands exist only in the neck region of the gallbladder, but none are present on our slides. The “hollowed out” epithelial-lined “pockets” which you may see on your slides represent blind recesses or diverticula of the folded epithelium that have been sectioned; they are not glands.
The lamina propria is a delicate loose connective tissue containing many small blood vessels. Occasionally, one can see a few smooth muscle fibers scattered within it, but a muscularis mucosae is lacking. The gallbladder also lacks a submucosa.
b. Muscularis - The smooth muscle of the muscularis forms interlacing and somewhat irregular bundles that may be cut longitudinally, transversely or obliquely. A fibroelastic network accompanies the muscle bundles. Perimuscular layer - External to the muscularis is the perimuscular layer of irregular connective tissue through which course the large blood vessels, nerves, and lymphatics that supply the organ. Here may be found collagenous and elastic fibers, fibroblasts, wandering lymphocytes, macrophages, fat cells and occasional small ganglia.
c. Perimuscular layer Serosa or fibrosa - External to the muscularis is the perimuscular The outermost layer of irregular connective tissue through which course the large blood vessels, nerves, and lymphatics that supply free surface of the organ. Here gallbladder is serosa (visceral peritoneum); it may be found collagenous and elastic fiberstorn off the section. Where the gallbladder attaches to the liver, fibroblasts, wandering lymphocytes, macrophages, fat cells and occasional small gangliaa fibrosa is present (seen on slide 152).
d. Serosa or fibrosa <peir-vm>UAB-Histology-00151</peir- The outermost layer of the free surface of the gallbladder is serosa (visceral peritoneum); it may be torn off the section. Where the gallbladder attaches to the liver, a fibrosa is present (seen on slide 152).vm> 2. === Slide 152 Liver and Gallbladder, (H&E)=== Portal canals and central veins show variations in size and are particularly well preserved. *The continuity of the sinusoidal lumens with the lumen of the central vein can be observed in many areas. *Several portal canal areas exhibit lymphocytic infiltration. *Hepatocytes are well preserved; many are binucleate.
a*Stellate cells (Kupffer cells) with visible cytoplasm and delicate cell processes can be observed. Portal canals and central veins show variations in size and are particularly well preserved These should be distinguished from the endothelial cells lining the sinusoid.
1) The continuity of the sinusoidal lumens Several portal vein branches are present in association with the lumen larger branches of the central vein can be observed in many areashepatic artery and bile duct (large portal canals).
2) Several portal canal areas exhibit lymphocytic infiltrationA portion of the gallbladder is attached to the liver.
3) Hepatocytes are well preserved; many are binucleateStudy the serosa of the liver and its relation to the serosa of the gallbladder.Is the serosa continuous?
4) Stellate cells (Kupffer cells) with visible cytoplasm and delicate cell processes can be observed. These should be distinguished from Identify the endothelial cells lining layers of the sinusoidgallbladder.
bObserve the area between the liver and gallbladder. Several portal vein branches are present in association This outer connective tissue layer of the gallbladder where it attaches to the liver is called the fibrosa; it merges with larger branches the connective tissue capsule of the hepatic artery and bile duct (large portal canals)liver.
c. A portion The simple columnar epithelium of the gallbladder is attached to the liverhighly absorptive and is well preserved in this section.
1) Study the serosa of the liver and its relation to the serosa of the gallbladder. Is the serosa continuous?<peir-vm>UAB-Histology-00152</peir-vm>
2) Identify the layers of the gallbladder.
3) Observe the area between the liver and gallbladder. This outer connective tissue layer of the gallbladder where it attaches to the liver is called the fibrosa; it merges with the connective tissue capsule of the liver.{{Template:Histologic}}
4) The simple columnar epithelium of the gallbladder is highly absorptive and is well preserved in this section.[[Category:Histologic]]